Fabrication of Highly Oriented Multilayer Films of Picene and DNTT on Their Bulklike Monolayer
- Chunyang ZhangChunyang ZhangFaculty of Pure and Applied Sciences, University of Tsukuba, 1-1-1 Tennodai, Tsukuba, Ibaraki 305-8573, JapanMore by Chunyang Zhang,
- Hiromu TsuboiHiromu TsuboiFaculty of Pure and Applied Sciences, University of Tsukuba, 1-1-1 Tennodai, Tsukuba, Ibaraki 305-8573, JapanMore by Hiromu Tsuboi,
- Yuri HasegawaYuri HasegawaInstitute for Molecular Science (IMS), National Institutes of Natural Sciences, 38 Nishigo-Naka, Myodaiji, Okazaki 444-8585, JapanMore by Yuri Hasegawa,
- Masato IwasawaMasato IwasawaFaculty of Pure and Applied Sciences, University of Tsukuba, 1-1-1 Tennodai, Tsukuba, Ibaraki 305-8573, JapanMore by Masato Iwasawa,
- Masahiro SasakiMasahiro SasakiFaculty of Pure and Applied Sciences, University of Tsukuba, 1-1-1 Tennodai, Tsukuba, Ibaraki 305-8573, JapanTsukuba Research Center for Energy Materials Science, University of Tsukuba, 1-1-1 Tennodai, Tsukuba, Ibaraki 305-8571, JapanMore by Masahiro Sasaki,
- Yutaka WakayamaYutaka WakayamaInternational Center for Materials Nanoarchitectonics (WPI-MANA), National Institute for Materials Science (NIMS), 1-1 Namiki, Tsukuba, Ibaraki 305-0044, JapanMore by Yutaka Wakayama,
- Hiroyuki IshiiHiroyuki IshiiFaculty of Pure and Applied Sciences, University of Tsukuba, 1-1-1 Tennodai, Tsukuba, Ibaraki 305-8573, JapanMore by Hiroyuki Ishii, and
- Yoichi Yamada*Yoichi Yamada*E-mail: [email protected]Faculty of Pure and Applied Sciences, University of Tsukuba, 1-1-1 Tennodai, Tsukuba, Ibaraki 305-8573, JapanMore by Yoichi Yamada
Copyright © 2019 American Chemical Society
Abstract
Highly oriented, multilayer molecular films of picene and dinaphtho[2,3-b:2′,3′-f]thieno[3,2-b]thiophene (DNTT) molecules with the long axis parallel to the substrate (parallel configuration, hereafter) were fabricated on their characteristic bulklike monolayer. These molecules form a dense monolayer with a bulklike molecular arrangement on metal surfaces such as Au(111), which allows further stacking of parallel molecules. Indeed, upon adsorption of picene and DNTT on these dense monolayers, growth of straight islands of multilayer without the dendritic layer was observed. Particularly, in the case of picene, one-dimensional islands with lengths over 100 μm were formed and aligned in 3-fold symmetric directions of the substrate, which was not observed in the case of DNTT. X-ray diffraction measurements revealed the presence of [201̅] and [211̅] planes and the absence of the [001] diffractions, indicating that the one-dimensional islands of picene indeed consist of parallel molecules. The formation of huge crystalline islands in the case of picene, in contrast to the case of DNTT, is likely induced by the stronger intermolecular force, as suggested from the calculation of the vibrational energy.
1. Introduction
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Small organic semiconductors with enhanced intermolecular interaction, such as phenacenes and thienoacenes, have been attracting attention because high-quality single crystals or thin films are expected. In this study, we focused on picene and dinaphtho[2,3-b:2′,3′-f]thieno[3,2-b]thiophene (DNTT) (as shown in the insets of Figure 1a,d) as model molecules of phenacenes and thienoacenes, respectively. Indeed, the single-crystalline picene shows significant dispersion of the highest occupied molecular orbital,(1,2) and organic field-effect transistors (OFETs) utilizing the single-crystalline picene exhibit high carrier mobility of more than 1 cm2 V–1 s–1.(3) Theoretical calculations have suggested that the single-crystalline picene can exhibit a maximum mobility up to 2.6 cm2 V–1 s–1 along the π–π stacking direction.(4) OFETs based on single-crystalline DNTT have shown mobility as high as 10 cm2 V–1 s–1.(5) However, OFETs utilizing the thin films of these molecules have exhibited much lower hole mobility, such as 0.1–0.3 cm2 V–1 s–1 for picene(6) and 2.9 cm2 V–1 s–1 for DNTT.(7) These facts suggest that further optimization of the thin-film structure of these organic semiconductors is required.
Figure 1
Figure 1. (a, d) Schematic images of molecular arrangement of the (110) plane of bulk picene and DNTT, respectively. (b, c) Scanning tunneling microscopy (STM) images of the picene monolayer on the Au(111) substrate. (e, f) STM images of the DNTT monolayer on the Au(111) substrate.
There have been common problems in the growth of the multilayer film of these π-conjugated planar molecules; the monolayers of these molecules on the flat substrates usually take a “flat-lying” or “face-on” conformation due to significant coupling between π orbital of molecules and the surface electronic states, whereas the second layer does not usually follow the configuration of the monolayers and tends to “stand up”. This mechanism usually leads to a dendritic growth of the multilayer with a complicated morphology and small domain sizes.(8−11) Even in the case of a carefully optimized deposition utilizing the supersonic molecular beam deposition of picene, the reported grain size of the film is in the range of several micrometers.(12) We focus here on the morphology of the monolayer, which is known to be one of the key features determining the structure of multilayer films of organic semiconductors.(13) We have recently reported that the careful deposition of picene and DNTT on flat surfaces can form a corrugated monolayer in which half of the molecules take a “side-on” geometry.(14) The same growth feature can also be seen in other phenacenes.(15) The molecular ordering of the monolayer resembles the (110) plane of the bulk crystal, although they are not identical, which is distinct from the case of the similar π-conjugated molecules such as pentacene, and this phenomenon should reflect the strong intermolecular interaction of these molecules. The bulklike monolayers could be useful for further stacking of parallel molecules on it, which can potentially yield a high-quality multilayer film.
Therefore, in this work, we have tried to grow the multilayer picene and DNTT on their peculiar monolayer. We indeed demonstrated here that the careful fabrication of the bulklike monolayers and further slow deposition of molecules resulted in formation of extremely long (more than 100 μm in the case of picene) and unidirectional islands consisting of parallel molecules. We will emphasize that much better crystalline films have been realized using picenes in comparison with DNTT. The superior growth found in picene films may be attributed to the stronger intermolecular force constant, as suggested from the analysis of the normal vibrational modes of the single-crystalline structure of these molecules. We note here that, upon the submission of the present article, we have been aware of the demonstration of the same strategy by Dreher et al. for the case of DNTT,(16) reporting consistent results with those discussed in the present work. The growth of the parallel molecules, which is particularly efficient for small molecules with enhanced intermolecular interaction such as phenacenes, will be beneficial not only for the applications in organic electronics devices but also in the basic research of the structure–function relationship of organic semiconductors.
2. Experimental and Theoretical Methods
ARTICLE SECTIONS
Single-crystalline Au(111) was used as a substrate. The substrate was cleaned by several cycles of Ar+ ion sputtering followed by annealing at approximately 400 °C. The cleanliness of the substrate was examined by low-energy electron diffraction (LEED) and scanning tunneling microscopy (STM) with a constant current mode. Sharp diffraction spots and herringbone reconstruction(17) of the Au(111) substrates were clearly observed by LEED and STM images. The deposition of picene and DNTT molecules on the clean Au(111) substrate was performed in an ultrahigh vacuum (UHV) environment of about 1 × 1010 Torr with a homemade Knudsen cell, which allows a slow deposition rate of approximately 1 ML/1000 s at room temperature to ensure good crystallinity of the resultant film. The deposition rate was monitored by a quartz crystal microbalance. The distance from the molecule evaporator to the Au(111) substrate was 35 cm. The formation of monolayers of picene and DNTT was confirmed by LEED and STM observation. After that, the multilayers of picene and DNTT were deposited on the well-ordered monolayer at the same rate in UHV. Structural measurements of the multilayer were performed ex situ at room temperature. The morphology of the multilayer was observed by atomic force microscopy (AFM) conducted in the tapping mode under atmospheric pressure and an optical microscope (OM). Crystallographic phase and molecular orientation in the film were characterized by X-ray diffraction (XRD) measurement, which was performed by a Cu Kα source X-ray of λ = 0.15406 nm. The normal vibrational modes of the crystal are obtained from the dynamical matrix constructed by the force field MMFF94s(18) using the CONFLEX code.(22) Here, the optimization process starts with the experimental structure, and the atomic positions are optimized at fixed lattice constants.
3. Results and Discussion
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First, we confirmed the formation of characteristic corrugated monolayers of picene and DNTT on a clean Au(111) substrate. It was seen that the picene and DNTT molecules adsorb in the flat-lying geometry at low coverage, whereas the geometry transforms into a corrugated arrangement near the monolayer coverage.(14)Figure 1b,e shows the monolayer structure of picene and DNTT on Au(111). As seen in the magnified STM image in Figure 1c,f, the molecules in the monolayer show corrugated arrangements with the unit cell sizes of 1.1 × 1.4 nm2 for picene and 1.1 × 1.6 nm2 for DNTT. For both molecules, it was found that the molecular rows (defined with black arrows in the STM images) of the dense phase were aligned along the symmetric ⟨11̅0⟩ direction of the substrate. Thus, there were three rotational domains, which were rotated by 120° from each other. The molecular arrangements and the sizes of the unit cells of the corrugated phases of picene and DNTT are apparently similar to the (110) planes of their single crystals (as illustrated in Figure 1a and d, respectively) although they are not identical. The formation of this type of bulklike monolayer seems to be common for phenacene or thienoacene, with enhanced intermolecular interaction.(19,20)
The dense monolayers of picene and DNTT with bulklike molecular arrangement as discussed above are promising for enhanced stacking of further molecules in a similar fashion. Therefore, we further deposited the multilayer of picene onto the dense monolayer and observed an abrupt growth of large and straight islands of the multilayer. These islands became so large that they could be clearly seen even with an optical microscope (OM). The OM images of the surface with low and high coverage of the picene islands prepared with the slow deposition of approximately 20 and 70 ML of picene molecules on the dense monolayer are shown in Figure 2a and b, respectively. In the image of the 20 ML coverage, Figure 2a, the formation of the rodlike picene crystalline islands with sharp edges is seen. The typical length, width, and height of the rod are approximately 30 μm, 0.5 μm, and 150 nm, respectively. It was clearly observed that the rods tend to align along three particular directions. The three directions, marked with arrows in Figure 2a, were found to correspond to the three domains of molecular rows of the monolayer on the Au(111) substrate,(21) that is, the ⟨11̅0⟩ direction. On increasing the coverage of molecules, as shown in Figure 2b, large-scale crystalline islands with a length of much more than 100 μm were obtained. At the same time, the domain with the aligned islands became as large as 0.5 mm. Figure 2c shows the AFM topography of the top surface of the crystalline picene island, where a step-terrace-like structure was observed. However, most of the steps were with a height of more than 5 nm, as shown in the line scan A in Figure 2c,d, much larger than a single molecular step, possibly due to bunching of the steps. In addition, the terrace morphology was found to be corrugated with amplitude of several nanometers as shown in the line scan B in Figure 2e. It is noted that the AFM measurements were conducted after taking the sample out to the atmospheric environment from a UHV; therefore, some distortion of the crystal surface, such as dewetting or disordering due to water coadsorption, may have occurred in this process. We note here that the structure of the monolayer was not changed on increasing the coverage of the molecule. Therefore, crystalline islands seem to form directly on the monolayer without the wetting layer.
Figure 2
Figure 2. (a, b) Optical microscope pictures of picene thin films with thicknesses of 20 and 70 ML, respectively; (c) AFM topography of the picene crystalline island. (d, e) Height profile along the scanning line A and line B of the AFM image.
We also examined the thicker film of DNTT on its bulklike monolayer. Figure 3a shows the OM image of the DNTT thin film with the molecular coverage of 30 ML. Although we observed formation of similar islands with the height of 130 nm (as shown in the line scan in Figure 3c,d) as in the case of picene, their sizes were relatively smaller and the tendency of the alignment of the islands with respect to the substrate was also weaker. At the higher coverage of 70 ML, as shown in Figure 3b, we found a network structure of the island with typical length of several micrometers, which was distinct from the case of the high-coverage picene (Figure 2b). From the AFM image shown in Figure 3c, the surface of the DNTT crystal island is rather rough. These results are consistent with the recent work of Dreher et al.(16)
Figure 3
Figure 3. (a, b) Optical microscope images of the DNTT thin film with coverages of 30 and 70 ML, respectively; (c) AFM topography of the DNTT crystalline island. (d) Height profile along the scanning line B of (c).
We then analyzed the molecular orientation of the crystalline picene film by means of XRD measurements. Figure 4a displays the spectrum of the θ/2θ scan without subtraction of the background signal of an Au substrate. Within the analyzed angular range of 5–30°, two obvious diffraction peaks were observed at 2θ = 22.1° and 2θ = 26.4°. These peaks are assigned to be due to (201̅) and (211̅) planes, respectively, in comparison with the powder spectra (Figure 4b). The schematic images of molecular arrangements of the (201̅) and (211̅) planes are illustrated in Figure 4c, which reveals a characteristic orientation of molecules with the long axes parallel to the surface (parallel molecule). Note that the molecular arrangements in the (201̅) and (211̅) planes are not identical to the monolayer. This implies that, although the bulklike monolayer can facilitate the further stacking of the parallel molecules, the template effect of the monolayer is not strong enough to realize epitaxial growth of the overlayer. In the case of DNTT, as revealed by the work of Dreher et al., the DNTT island showed a (121̅) plane in the XRD spectrum, which also shows a similar but distinct molecular arrangement from its monolayer.
Figure 4
Figure 4. (a) XRD spectrum of the picene thin film on Au(111). (b) Calculated spectrum of the picene powder performed by the CCSD software package. (c) Model of molecular arrangements of the (201̅) and (211̅) planes of the bulk picene crystal.
Although we demonstrated that both picene and DNTT can form the crystalline islands with parallel molecules, that of picene showed a higher degree of homogeneity of each island, strict orientation with respect to the substrate, and a tendency to form larger domains with single orientation of crystalline islands. Although a microscopic understanding of the crystallization mechanism is still a difficult issue, the different behavior between two molecules may be attributable to the difference in the intermolecular interactions. As the measure of the intermolecular force constant, we examined the vibrational energy of the translational modes with the molecular displacement in the direction of the van der Waals bonding, in the case of the single-crystalline picene and DNTT. Figure 5 shows the translational optic phonon modes at the Γ point, in which the displacements of atoms (indicated by red arrows) are mainly along the π-stacking direction of two adjacent molecules in the a–b plane of the single crystal. The vibrational energies of such modes in the case of picene and DNTT were found to be 10.61 and 8.638 meV, respectively, as indicated in the figure. From the energy of the vibrational modes and masses of the molecule (picene: 2.78 × 10–1 kg mol–1; DNTT: 3.40 × 10–1 kg mol–1), we estimated the force constant of the intermolecular van der Waals bonding, simply assuming the harmonic oscillation, deducing 30.1 kg s–2 for picene and 24.3 kg s–2 for DNTT. Thus, the π–π interaction in picene is found to be stronger than that of DNTT, possibly resulting in the better crystalline morphology of the multilayer. However, since the molecular growth can depend on many other parameters, further detailed examination will surely be required.
Figure 5
Figure 5. (a) Molecular vibration modes in the parallel ab plane of the DNTT dimer of its bulk phase unit cell. (b) Molecular vibration modes in the parallel ab plane of the picene dimer of its bulk phase unit cell. The parameters below the figures indicate their corresponding vibrational energy.
It is also noted that the similar straight islands of pentacene and quaterphenyl were previously found on the metal substrate.(13,23) However, the size of the islands was much smaller than the case of picene or DNTT. This difference is attributable to the difference in the structure of the monolayer, that is, the monolayer of pentacene consists of flat-lying molecules, in contrast to the case of molecules examined in the present study. The characteristic shape of the monolayer with a bulklike molecular arrangement can therefore be considered to stabilize the upper layer with the parallel molecules.
This crystalline film with parallel molecules may exhibit an enhanced π-stacking, and thus it will be beneficial not only for applications in organic electronics, but also for basic research of the structure–property relationships of these types of organic semiconductors.
4. Conclusions
ARTICLE SECTIONS
We fabricated well-defined crystalline films of picene and DNTT on their well-ordered monolayers with a bulklike molecular arrangement. By means of slow deposition of the multilayer on the bulklike monolayer, large-scale crystalline islands having lengths of several hundred micrometers were obtained, especially in the case of picene. XRD measurement revealed that picene crystals consist of planes of (201̅) and (211̅), clearly suggesting that the film consists of the parallel molecules which may be stabilized by the peculiar structure of the monolayer.
The authors declare no competing financial interest.
Author Information
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- Yoichi Yamada - Faculty of Pure and Applied Sciences, University of Tsukuba, 1-1-1 Tennodai, Tsukuba, Ibaraki 305-8573, Japan;
http://orcid.org/0000-0001-8187-3409;
- Chunyang Zhang - Faculty of Pure and Applied Sciences, University of Tsukuba, 1-1-1 Tennodai, Tsukuba, Ibaraki 305-8573, Japan;http://orcid.org/0000-0002-7287-5733
- Yutaka Wakayama - International Center for Materials Nanoarchitectonics (WPI-MANA), National Institute for Materials Science (NIMS), 1-1 Namiki, Tsukuba, Ibaraki 305-0044, Japan;http://orcid.org/0000-0002-0801-8884
The authors declare no competing financial interest.
Acknowledgments
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The authors are grateful to Mika Watanabe (NIMS, Wakayama Gr.) for her assistance with the XRD measurements. This work was supported by JSPS KAKENHI (Grant Numbers JP26286011, JP16K13678, and 15J05607). This work was partly performed under the approval of the Photon 436 Factory Program Advisory Committee (Proposal Nos. 2017G030 and 2018S2-005). One of the authors (C.Z.) would like to thank China Scholarship Council for the scholarship under the Chinese Government Graduate Student Overseas Study Scholarship Program.
References
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This article references 23 other publications.
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- 9Jariwala, D.; Howell, S. L.; Chen, K.-S.; Kang, J.; Sangwan, V. K.; Filippone, S. A.; Turrisi, R.; Marks, T. J.; Lauhon, L. J.; Hersam, M. C. Hybrid, Gate-Tunable, van Der Waals P–n Heterojunctions from Pentacene and MoS2. Nano Lett. 2016, 16, 497– 503, DOI: 10.1021/acs.nanolett.5b04141[ACS Full Text], [CAS], Google Scholar9https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2MXhvFylu7rN&md5=0d3108b97ad4678d4a68dea7599de957Hybrid, gate-tunable, van der Waals p-n heterojunctions from pentacene and MoS2Jariwala, Deep; Howell, Sarah L.; Chen, Kan-Sheng; Kang, Junmo; Sangwan, Vinod K.; Filippone, Stephen A.; Turrisi, Riccardo; Marks, Tobin J.; Lauhon, Lincoln J.; Hersam, Mark C.Nano Letters (2016), 16 (1), 497-503CODEN: NALEFD; ISSN:1530-6984. (American Chemical Society)The recent emergence of a wide variety of 2-dimensional materials has created new opportunities for device concepts and applications. In particular, the availability of semiconducting transition metal dichalcogenides, in addn. to semimetallic graphene and insulating boron nitride, has enabled the fabrication of "all 2-dimensional" van der Waals heterostructure devices. Furthermore, the concept of van der Waals heterostructures has the potential to be significantly broadened beyond layered solids. For example, mol. and polymeric org. solids, whose surface atoms possess satd. bonds, are also known to interact via van der Waals forces and thus offer an alternative for scalable integration with 2-dimensional materials. Here, the authors demonstrate the integration of an org. small mol. p-type semiconductor, pentacene, with a 2-dimensional n-type semiconductor, MoS2. The resulting p-n heterojunction is gate-tunable and shows asym. control over the antiambipolar transfer characteristic. In addn., the pentacene/MoS2 heterojunction exhibits a photovoltaic effect attributable to type II band alignment, which suggests that MoS2 can function as an acceptor in hybrid solar cells.
- 10Rockson, T. K.; Baek, S.; Jang, H.; Oh, S.; Choi, G.; Choi, H. H.; Lee, H. S. Macroscopic Interfacial Property as a Determining Parameter for Reliable Prediction of Charge Mobility in Organic Transistors. J. Phys. Chem. C 2018, 122, 17695– 17705, DOI: 10.1021/acs.jpcc.8b05959
- 11Wang, Q.; Jiang, S.; Qiu, L.; Qian, J.; Ono, L. K.; Leyden, M. R.; Wang, X.; Shi, Y.; Zheng, Y.; Qi, Y. Interfacial Flat-Lying Molecular Monolayers for Performance Enhancement in Organic Field-Effect Transistors. ACS Appl. Mater. Interfaces 2018, 10, 22513– 22519, DOI: 10.1021/acsami.8b07095[ACS Full Text], [CAS], Google Scholar11https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC1cXhtFSgsrnF&md5=e06dd5cbd4beafbc91108fb44f5b6634Interfacial flat-lying molecular monolayers for performance enhancement in organic field-effect transistorsWang, Qijing; Jiang, Sai; Qiu, Longbin; Qian, Jun; Ono, Luis K.; Leyden, Matthew R.; Wang, Xinran; Shi, Yi; Zheng, Youdou; Qi, Yabing; Li, YunACS Applied Materials & Interfaces (2018), 10 (26), 22513-22519CODEN: AAMICK; ISSN:1944-8244. (American Chemical Society)Org. field-effect transistors (OFETs) are the most fundamental device units in org. electronics. Interface engineering at the semiconductor/dielec. interface is an effective approach for improving device performance, particularly for enhancing charge transport in conducting channels. Here, the authors report flat-lying mol. monolayers that exhibit good uniformity and high crystallinity at the semiconductor/dielec. interface, deposited through slow thermal evapn. Transistor devices achieve high carrier mobility up to 2.80 cm2 V-1 s-1, which represents a remarkably improvement in device performance compared with devices that are completely based on fast-evapd. films. Interfacial flat-lying monolayers benefit charge transport by suppressing the polarization of dipoles and narrowing the broadening of trap d. of states. The work provides a promising strategy for enhancing the performance of OFETs by using interfacial flat-lying mol. monolayers.
- 12Gottardi, S.; Toccoli, T.; Iannotta, S.; Bettotti, P.; Cassinese, A.; Barra, M.; Ricciotti, L.; Kubozono, Y. Optimizing Picene Molecular Assembling by Supersonic Molecular Beam Deposition. J. Phys. Chem. C 2012, 116, 24503– 24511, DOI: 10.1021/jp304561s[ACS Full Text], [CAS], Google Scholar12https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC38XhsFOltr7O&md5=b828dd01f9b30975ddbe8404bc6a453dOptimizing Picene Molecular Assembling by Supersonic Molecular Beam DepositionGottardi, Stefano; Toccoli, Tullio; Iannotta, Salvatore; Bettotti, Paolo; Cassinese, Antonio; Barra, Mario; Ricciotti, Laura; Kubozono, YoshihiroJournal of Physical Chemistry C (2012), 116 (46), 24503-24511CODEN: JPCCCK; ISSN:1932-7447. (American Chemical Society)Here we report an investigation of the growth of picene by supersonic mol. beam deposition on thermal silicon oxide and on a self-assembled monolayer of hexamethyldisiloxane (HMDS). In both cases film morphol. shows a structure with very sharp island edges and well-sepd. islands which size and height depend on the deposition conditions. Picene films growth on bare silicon covered with hydrophobic HDMS shows islands characterized by large regular crystallites of several micrometers; on the other hand, films growth on silicon oxide shows smaller and thicker islands. We analyzed the details of the growth model and describe it as a balancing mechanism involving the weak interaction between mols. and surface and the strong picene-picene interaction that leads to a different Schwoebel-Ehrlich barrier in the first layer with respect to the successive one. Finally, we study the charge transport properties of these films by fabricating field-effect transistors devices in both top and bottom contact configuration. We notice that substrate influences the elec. properties of the device and we obtained a max. mobility value of 1.2 cm2 V-1 s-1 measured on top contact devices in air.
- 13Käfer, D.; Ruppel, L.; Witte, G. Growth of Pentacene on Clean and Modified Gold Surfaces. Phys. Rev. B 2007, 75, 085309 DOI: 10.1103/PhysRevB.75.085309[Crossref], [CAS], Google Scholar13https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD2sXislarur0%253D&md5=0c6a3128acc3c811a7575ed3c79fff9fGrowth of pentacene on clean and modified gold surfacesKafer, Daniel; Ruppel, Lars; Witte, GregorPhysical Review B: Condensed Matter and Materials Physics (2007), 75 (8), 085309/1-085309/14CODEN: PRBMDO; ISSN:1098-0121. (American Physical Society)The growth and evolution of pentacene films on Au substrates were studied. By combining complementary techniques including scanning tunneling microscopy, at. force microscopy, SEM, near-edge x-ray-absorption fine structure, and x-ray diffraction, the mol. orientation, cryst. structure, and morphol. of the org. films were characterized as a function of film thickness and growth parameters (temp. and rate) for different Au substrates ranging from Au(111) single crystals to polycryst. Au. Also, the influence of precoating the various Au substrates with self-assembled monolayers (SAM's) of organothiols with different chem. terminations was studied. On bare Au the growth of pentacene films is characterized by a pronounced dewetting while the mol. orientation within the resulting cryst. 3-dimensional islands depends distinctly on the roughness and cleanliness of the substrate surface. After completion of the 1st wetting layer where mols. adopt a planar orientation parallel to the surface the mols. continue to grow in a tilted fashion: on Au(111) the long mol. axis is oriented parallel to the surface while on polycryst. Au it is upstanding oriented and thus parallels the cryst. orientation of pentacene films grown on SiO2. On SAM pretreated Au substrates the formation of a wetting layer is effectively suppressed and pentacene grows in a quasi-layer-by-layer fashion with an upstanding orientation leading to rather smooth films. The latter growth mode is obsd. independently of the chem. termination of the SAM's and the roughness of the Au substrate. Possible reasons for the different growth mechanism as well as consequences for the assignment of spectroscopic data of thin pentacene film are discussed.
- 14Hasegawa, Y.; Yamada, Y.; Hosokai, T.; Koswattage, K. R.; Yano, M.; Wakayama, Y.; Sasaki, M. Overlapping of Frontier Orbitals in Well-Defined Dinaphtho[2,3-b:2′,3′-f]Thieno[3,2- b ]-Thiophene and Picene Monolayers. J. Phys. Chem. C 2016, 120, 21536– 21542, DOI: 10.1021/acs.jpcc.6b06838
- 15Chen, S.-W.; Sang, I.-C.; Okamoto, H.; Hoffmann, G. Adsorption of Phenacenes on a Metallic Substrate: Revisited. J. Phys. Chem. C 2017, 121, 11390– 11398, DOI: 10.1021/acs.jpcc.7b01806[ACS Full Text], [CAS], Google Scholar15https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2sXntFaqurc%253D&md5=0084d47a09467a7192a2141428c146beAdsorption of Phenacenes on a Metallic Substrate: RevisitedChen, Song-Wen; Sang, I-Chen; Okamoto, Hideki; Hoffmann, GermarJournal of Physical Chemistry C (2017), 121 (21), 11390-11398CODEN: JPCCCK; ISSN:1932-7447. (American Chemical Society)Phenacenes represent a class of simple hydrocarbons with appealing phys. properties ranging from high charge mobility to supercond. in combination with chem. robustness that are easily modified to serve as versatile building blocks for tailored structures. As a promising candidate for applications in org. devices, phenacenes are the focus of recent investigations. Thereby, the initial growth behavior starting from a single mol. is controversial. Here, we address the growth of [7]phenacene and [9]phenacene on a Ag(111) surface, studying the details of the initial stage of growth by scanning tunneling microscopy. According to our results, a previously introduced model involving a coverage-dependent phase change with the out-of-plane rotation of mols. in the initial growth stage can be disregarded. Instead, we find evidence for the formation of a new phase on top of an in-plane wetting layer during the initial stage of growth.
- 16Dreher, M.; Bischof, D.; Widdascheck, F.; Huttner, A.; Breuer, T.; Witte, G. Interface Structure and Evolution of Dinaphthothienothiophene (DNTT) Films on Noble Metal Substrates. Adv. Mater. Interfaces 2018, 1800920 DOI: 10.1002/admi.201800920
- 17Hanke, F.; Björk, J. Structure and Local Reactivity of the Au(111) Surface Reconstruction. Phys. Rev. B 2013, 87, 235422 DOI: 10.1103/PhysRevB.87.235422[Crossref], [CAS], Google Scholar17https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC3sXht1ClsL%252FI&md5=b9d87b94f06d5ca1a32379398b711b5dStructure and local reactivity of the Au(111) surface reconstructionHanke, Felix; Bjork, JonasPhysical Review B: Condensed Matter and Materials Physics (2013), 87 (23), 235422/1-235422/6CODEN: PRBMDO; ISSN:1098-0121. (American Physical Society)The close-packed (111) surface of gold is well known to show a 22 × √3 reconstruction on single nm lengths with a long-range herringbone pattern on scales of a few hundred nm. Here we investigate the local reconstruction using d. functional theory and compare the results to scanning tunneling microscopy expts. Moreover, we use hydrogen and fluorine as probe atoms to investigate changes in the ability of the Au(111) surface to catalyze the reactions involved in the formation of mol. nanostructures. We find a small variation of the reactivity across different surface sites and link those results to the local coordination environment of the face-centered-cubic (fcc), hexagonal-close-packed (hcp), and ridge regions. Finally, we scrutinize a commonly used approxn. in d. functional studies, namely that Au(111) is atomically flat and a perfect termination of the fcc lattice.
- 18Halgren, T. A. Merck Molecular Force Field. I. Basis, Form, Scope, Parameterization, and Performance of MMFF94. J. Comput. Chem. 1996, 17, 490– 519, DOI: 10.1002/(SICI)1096-987X(199604)17:5/6<490::AID-JCC1>3.0.CO;2-P[Crossref], [CAS], Google Scholar18https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADyaK28XhvVGmsbk%253D&md5=56fb073477b4f49d1dfbd786fc56a480Merck molecular force field. I. Basis, form, scope, parameterization, and performance of MMFF94Halgren, Thomas A.Journal of Computational Chemistry (1996), 17 (5 & 6), 490-519CODEN: JCCHDD; ISSN:0192-8651. (Wiley)This article introduces MMFF94, the initial published version of the Merck mol. force field (MMFF). It describes the objectives set for MMFF, the form it takes, and the range of systems to which it applies. This study also outlines the methodol. employed in parameterizing MMFF94 and summarizes its performance in reproducing computational and exptl. data. Though similar to MM3 in some respects, MMFF94 differs in ways intended to facilitate application to condensed-phase processes in mol.-dynamics simulations. Indeed, MMFF94 seeks to achieve MM3-like accuracy for small mols. in a combined "org./protein" force field that is equally applicable to proteins and other systems of biol. significance. A second distinguishing feature is that the core protion of MMFF94 has primarily been derived from high-quality computational data-ca. 500 mol. structures optimized at the HF/6-31G* level, 475 structures optimized at the MP2/6-31G* level, 380 MP2/6-31* structures evaluated at a defined approxn. to the MP4SDQ/TZP level, and 1450 structures partly derived from MP2/6-31G* geometries and evaluated at the MP2/TZP level. A third distinguishing feature is that MMFF94 has been parameterized for a wide variety of chem. systems of interest to org. and combinations of functional groups for which little, if any, useful exptl. data are available. The methodol. used in parameterizing MMFF94 represents a fourth distinguishing feature. Rather than using the common "functional group" approach, nearly all MMFF parameters have been detd. in a mutually consistent fashion from the full set of available computational data. MMFF94 reproduces the computational data used in its parameterization very well. In addn., MMFF94 reproduces exptl. bond lengths (0.014 Å root mean square [rms]), bond angles (1.2° rms), vibrational frequencies (61 cm-1 rms), conformational energies (0.38 kcal/mol rms), and rotational barriers (0.39 kcal/mol rms) very nearly as well as does MM3 for comparable systems. MMFF94 also describes intermol. interactions in hydrogen-bonded systems in a way that closely parallels that given by the highly regarded OPLS force field.
- 19Yano, M.; Okada, R.; Endo, M.; Shimizu, R.; Hasegawa, Y.; Yamada, Y.; Sasaki, M. Microscopic Structure of K-Doped Organic Monolayers. e-J. Surf. Sci. Nanotechnol. 2014, 12, 330– 333, DOI: 10.1380/ejssnt.2014.330[Crossref], [CAS], Google Scholar19https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2cXhs12ksrjL&md5=c8dc3473413fd364d8c47c2666b6e5b6Microscopic structure of K-doped organic monolayersYano, Masahiro; Okada, Ryosuke; Endo, Megumi; Shimizu, Ryosuke; Hasegawa, Yuri; Yamada, Yoichi; Sasaki, Masahiroe-Journal of Surface Science and Nanotechnology (2014), 12 (), 330-333CODEN: SSNUA9; ISSN:1348-0391. (Surface Science Society of Japan)Potassium (K) adsorption on coronene, picene and [6]phenacene monolayers, which serves as a model system for the metal-intercalated arom. superconductors, was studied in a mol. scale. Scanning tunneling microscopy (STM) on the K-doped monolayers revealed drastic rearrangements of the mol. layers. Besides the overall similarity of the mol. arrangement in the doped phase, fine structures and unit cell sizes were different, depending on the host mols. The overall similarity in the structures of the K-doped monolayers should be in close relation to the supercond. on these systems.
- 20Wang, Q.; Xin, Q.; Wang, R.-B.; Oehzelt, M.; Ueno, N.; Kera, S.; Duhm, S. Picene Thin Films on Metal Surfaces: Impact of Molecular Shape on Interfacial Coupling: Picene Thin Films on Metal Surfaces. Phys. Status Solidi RRL 2017, 11, 1700012 DOI: 10.1002/pssr.201700012
- 21Simbrunner, C. Epitaxial Growth of Sexi-Thiophene and Para-Hexaphenyl and Its Implications for the Fabrication of Self-Assembled Lasing Nano-Fibres. Semicond. Sci. Technol. 2013, 28, 053001 DOI: 10.1088/0268-1242/28/5/053001[Crossref], [CAS], Google Scholar21https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC3sXnsVKjsrw%253D&md5=e4bc6bf171a73f9bcd46b8dc29cfcbb9Epitaxial growth of sexi-thiophene and para-hexaphenyl and its implications for the fabrication of self-assembled lasing nano-fibresSimbrunner, ClemensSemiconductor Science and Technology (2013), 28 (5), 053001, 31 pp.CODEN: SSTEET; ISSN:0268-1242. (IOP Publishing Ltd.)A review. Over the last few years, epitaxially grown self-assembled org. nano-structures became of increasing interest due to their high potential for implementation within opto-electronic devices. Exemplarily, the epitaxial growth of the rod-like mols. para-hexaphenyl (p-6P) and α-sexi-thiophene (6T) is discussed within this review. Both mols. tend to crystallize in highly asym. elongated entities which are also called nano-fibers. It is demonstrated that the obtained needle orientations and morphologies result from a complex interplay between various parameters, e.g., substrate surface symmetry, mol. adsorption, crystal structure and contact plane. The interplay and its implications on the fabrication of self-assembled waveguiding nano-fibers and optical resonator structures are discussed and substantiated by a comparison with the reported literature. In further consequence, it is demonstrated that a precise control on the mol. adsorption geometry and the crystal contact plane represents a fundamental key parameter for the fabrication of self-assembled nano-fibers. As both parameters are basically detd. by the chosen mol.-substrate material couple, the possible spectrum of mol. building blocks for the fabrication of waveguiding and lasing nano-structures can be predicted by the discussed growth model. A possible expansion of this common valid concept is presented by the utilization of org.-org. heteroepitaxy. Based on the reported p-6P/6T heterostructures which have been fabricated on various substrate surfaces, it is substantiated that the fabrication of org.-org. interfaces can be effectively used to gain control on the mol. adsorption geometry. As the proposed strategy still lacks a precise control of the obtained crystal contact plane, further strategies are discussed which potentially lead to a controlled fabrication of opto-electronic devices based on self-assembled org. nano-structures.
- 22Goto, H.; Obata, S.; Nakayama, N.; Ohta, K. CONFLEX8; Conflex: Tokyo, Japan, 2017.Google ScholarThere is no corresponding record for this reference.
- 23Müllegger, S.; Salzmann, I.; Resel, R.; Hlawacek, G.; Teichert, C.; Winkler, A. Growth Kinetics, Structure, and Morphology of Para-Quaterphenyl Thin Films on Gold(111). J. Chem. Phys. 2004, 121, 2272– 2277, DOI: 10.1063/1.1767154[Crossref], [PubMed], [CAS], Google Scholar23https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD2cXlslOmsbs%253D&md5=4074d4435fbb4334a5ff3af436432338Growth kinetics, structure, and morphology of para-quaterphenyl thin films on gold(111)Mullegger, S.; Salzmann, I.; Resel, R.; Hlawacek, G.; Teichert, C.; Winkler, A.Journal of Chemical Physics (2004), 121 (5), 2272-2277CODEN: JCPSA6; ISSN:0021-9606. (American Institute of Physics)The adsorption, desorption, and growth kinetics as well as the thin film morphol. and crystal structure of p-quaterphenyl (4P) grown under ultrahigh vacuum conditions on single cryst. Au(111) have been investigated. Thermal desorption spectroscopy (TDS) reveals two distinct first-order peaks attributed to monolayer desorption followed by a zero-order multilayer desorption. The satn. coverage of the full 4P monolayer has been quant. measured with a quartz microbalance to be 8×1013 mols./cm2. Using LEED the structures of the 0.5 and 1 ML (monolayer) adsorbates have been studied, showing highly regular arrangements of the 4P mols., which are affected by the (111) surface structure. At the transition from 0.5 to 1 ML a structural compression of the overlayer has been obsd. The behavior of thicker 4P films has been investigated by combined TDS-XPS (XPS-XPS). A temp.-induced recrystn. process at about 270 K has been obsd. for a 7 nm thick 4P film grown at 93 K, corresponding to a transition from a disordered layerlike growth to a cryst. island growth. Ex situ optical microscopy and at.-force microscopy investigations have revealed needle-shaped 4P islands. Applying x-ray diffraction the cryst. order and epitaxial relationship of the 4P films with 30 nm and 200 nm mean thicknesses have been detd.
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- Balu Balambiga, Ramachandran Dheepika, Paneerselvam Devibala, Predhanekar Mohamed Imran, Samuthira Nagarajan. Picene and PTCDI based solution processable ambipolar OFETs. Scientific Reports 2020, 10 (1) https://doi.org/10.1038/s41598-020-78356-5
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Abstract
Figure 1
Figure 1. (a, d) Schematic images of molecular arrangement of the (110) plane of bulk picene and DNTT, respectively. (b, c) Scanning tunneling microscopy (STM) images of the picene monolayer on the Au(111) substrate. (e, f) STM images of the DNTT monolayer on the Au(111) substrate.
Figure 2
Figure 2. (a, b) Optical microscope pictures of picene thin films with thicknesses of 20 and 70 ML, respectively; (c) AFM topography of the picene crystalline island. (d, e) Height profile along the scanning line A and line B of the AFM image.
Figure 3
Figure 3. (a, b) Optical microscope images of the DNTT thin film with coverages of 30 and 70 ML, respectively; (c) AFM topography of the DNTT crystalline island. (d) Height profile along the scanning line B of (c).
Figure 4
Figure 4. (a) XRD spectrum of the picene thin film on Au(111). (b) Calculated spectrum of the picene powder performed by the CCSD software package. (c) Model of molecular arrangements of the (201̅) and (211̅) planes of the bulk picene crystal.
Figure 5
Figure 5. (a) Molecular vibration modes in the parallel ab plane of the DNTT dimer of its bulk phase unit cell. (b) Molecular vibration modes in the parallel ab plane of the picene dimer of its bulk phase unit cell. The parameters below the figures indicate their corresponding vibrational energy.
References
ARTICLE SECTIONSThis article references 23 other publications.
- 1Xin, Q.; Duhm, S.; Bussolotti, F.; Akaike, K.; Kubozono, Y.; Aoki, H.; Kosugi, T.; Kera, S.; Ueno, N. Accessing Surface Brillouin Zone and Band Structure of Picene Single Crystals. Phys. Rev. Lett. 2012, 108, 226401 DOI: 10.1103/PhysRevLett.108.226401[Crossref], [PubMed], [CAS], Google Scholar1https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC38XpvV2ksL4%253D&md5=05e7f2fd1bb00661de55ed055a6f2f64Accessing surface Brillouin zone and band structure of picene single crystalsXin, Qian; Duhm, Steffen; Bussolotti, Fabio; Akaike, Kouki; Kubozono, Yoshihiro; Aoki, Hideo; Kosugi, Taichi; Kera, Satoshi; Ueno, NobuoPhysical Review Letters (2012), 108 (22), 226401/1-226401/5CODEN: PRLTAO; ISSN:0031-9007. (American Physical Society)We have exptl. revealed the band structure and the surface Brillouin zone of insulating picene single crystals (SCs), the mother org. system for a recently discovered arom. superconductor, with UPS (UPS) and LEED with a laser for photoconduction. A hole effective mass of 2.24m0 and the hole mobility μh ≥ 9.0 cm2/V s (298 K) were deduced in the Γ-Y direction. We have further shown that some picene SCs did not show charging during UPS even without the laser, which indicates that pristine UPS works for high-quality org. SCs.
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- 3Kawai, N.; Eguchi, R.; Goto, H.; Akaike, K.; Kaji, Y.; Kambe, T.; Fujiwara, A.; Kubozono, Y. Characteristics of Single Crystal Field-Effect Transistors with a New Type of Aromatic Hydrocarbon, Picene. J. Phys. Chem. C 2012, 116, 7983– 7988, DOI: 10.1021/jp300052p[ACS Full Text], [CAS], Google Scholar3https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC38Xkt1OlsLk%253D&md5=67151f97cf264733d4fed9b6b617af3aCharacteristics of single crystal field-effect transistors with new type of aromatic hydrocarbon, piceneKawai, Nobuyuki; Eguchi, Ritsuko; Goto, Hidenori; Akaike, Kouki; Kaji, Yumiko; Kambe, Takashi; Fujiwara, Akihiko; Kubozono, YoshihiroJournal of Physical Chemistry C (2012), 116 (14), 7983-7988CODEN: JPCCCK; ISSN:1932-7447. (American Chemical Society)Picene is a phenacene-type arom. hydrocarbon mol. with five benzene rings. We have fabricated picene single crystal (SC) field-effect transistors (FETs) with solid gate and ionic liq. gate dielecs. Although the picene SC FET showed a large hole-injection barrier without any modification of interface between source/drain electrodes and picene SC, such a large hole-injection barrier could be effectively reduced by modifying the interface with tetracyanoquinodimethane (TCNQ). Picene SC FET with an HfO2 gate dielec. and TCNQ-coated electrodes shows p-channel characteristics with a smooth hole injection and a field-effect mobility more than 1 cm2 V-1 s-1 in two-terminal measurement. Picene SC FET could be operated even in bottom-contact structure by modifying the interface with octanethiol. Furthermore, picene SC FET operated with ionic liq. gate dielec., 1-butyl-3-Me imidazolium hexafluorophosphate, showing the field-effect mobility of 1.8 × 10-1 cm2 V-1 s-1 and low abs. value, 1.9 V, of threshold voltage.
- 4Nguyen, T. P.; Shim, J. H.; Lee, J. Y. Density Functional Theory Studies of Hole Mobility in Picene and Pentacene Crystals. J. Phys. Chem. C 2015, 119, 11301– 11310, DOI: 10.1021/jp511484d[ACS Full Text], [CAS], Google Scholar4https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2MXnsVeisrs%253D&md5=5eb2ea9737a718c39bf124966b7d2b1eDensity Functional Theory Studies of Hole Mobility in Picene and Pentacene CrystalsNguyen, Thao P.; Shim, Ji Hoon; Lee, Jin YongJournal of Physical Chemistry C (2015), 119 (21), 11301-11310CODEN: JPCCCK; ISSN:1932-7447. (American Chemical Society)We have investigated the electronic properties and hole mobilities of picene and its isomer pentacene using the d. functional theory and classical Marcus charge transfer theory. In pristine crystal with herringbone structure, pentacene and picene have drift hole mobilities of 2.147 and 0.644 cm2 V-1 s-1, resp., which are consistent with recent exptl. results. We also show that picene crystal can exhibit max. mobility up to 2.629 cm2 V-1 s-1 along the π-π stacking direction, while the highest mobility of pentacene crystal exhibits along the herringbone stacking direction. Also the anisotropy of the mobility in the ab plane is 2.4 and 5.6 for picene and pentacene crystals, resp. Since the air stability of picene is better than pentacene due to lower HOMO levels in picene, we suggest that picene and its homologous phenacenes series are promising candidates toward high mobility org. semiconductor devices with good air stability. This work also sheds light on the favorable or undesirable properties for efficient charge transport in oligoacene and phenacenes series.
- 5Xie, W.; Willa, K.; Wu, Y.; Häusermann, R.; Takimiya, K.; Batlogg, B.; Frisbie, C. D. Temperature-Independent Transport in High-Mobility Dinaphtho-Thieno-Thiophene (DNTT) Single Crystal Transistors. Adv. Mater. 2013, 25, 3478– 3484, DOI: 10.1002/adma.201300886[Crossref], [PubMed], [CAS], Google Scholar5https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC3sXnvFSgsrs%253D&md5=7c33983ebcbd13996490ca00135da964Temperature-Independent Transport in High-Mobility Dinaphtho-Thieno-Thiophene (DNTT) Single Crystal TransistorsXie, Wei; Willa, Kristin; Wu, Yanfei; Haeusermann, Roger; Takimiya, Kazuo; Batlogg, Bertram; Frisbie, C. DanielAdvanced Materials (Weinheim, Germany) (2013), 25 (25), 3478-3484CODEN: ADVMEW; ISSN:0935-9648. (Wiley-VCH Verlag GmbH & Co. KGaA)Authors report a record hole mobility approaching 10 cm2V-1s-1 in vapor-grown DNTT single crystals with the vacuum-gap FET architecture. Importantly, their careful four-terminal variable temp. measurements reveal temp. independent behavior of the hole mobility below room temp. Weak mobility anisotropy and very low trap d. of states are also obsd. for DNTT. Combining a comprehensive study of structural properties, temp. dependent elec. measurements, and simulations, they find DNTT single crystals to be a very promising platform for future fundamental studies of charge transport in org. semiconductors.
- 6Diallo, A. K.; Kurihara, R.; Yoshimoto, N.; Videlot-Ackermann, C. Morphology and Microstructure of Picene Thin-Films for Air-Operating Transistors. Appl. Surf. Sci. 2014, 314, 704– 710, DOI: 10.1016/j.apsusc.2014.07.085
- 7Yamamoto, T.; Takimiya, K. Facile Synthesis of Highly π-Extended Heteroarenes, Dinaphtho[2,3- b:2′,3′- f ]Chalcogenopheno[3,2- b ]Chalcogenophenes, and Their Application to Field-Effect Transistors. J. Am. Chem. Soc. 2007, 129, 2224– 2225, DOI: 10.1021/ja068429z
- 8Ding, Z.; Abbas, G. A.; Assender, H. E.; Morrison, J. J.; Sanchez-Romaguera, V.; Yeates, S. G.; Taylor, D. M. Improving the Performance of Organic Thin Film Transistors Formed on a Vacuum Flash-Evaporated Acrylate Insulator. Appl. Phys. Lett. 2013, 103, 233301 DOI: 10.1063/1.4839275
- 9Jariwala, D.; Howell, S. L.; Chen, K.-S.; Kang, J.; Sangwan, V. K.; Filippone, S. A.; Turrisi, R.; Marks, T. J.; Lauhon, L. J.; Hersam, M. C. Hybrid, Gate-Tunable, van Der Waals P–n Heterojunctions from Pentacene and MoS2. Nano Lett. 2016, 16, 497– 503, DOI: 10.1021/acs.nanolett.5b04141[ACS Full Text], [CAS], Google Scholar9https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2MXhvFylu7rN&md5=0d3108b97ad4678d4a68dea7599de957Hybrid, gate-tunable, van der Waals p-n heterojunctions from pentacene and MoS2Jariwala, Deep; Howell, Sarah L.; Chen, Kan-Sheng; Kang, Junmo; Sangwan, Vinod K.; Filippone, Stephen A.; Turrisi, Riccardo; Marks, Tobin J.; Lauhon, Lincoln J.; Hersam, Mark C.Nano Letters (2016), 16 (1), 497-503CODEN: NALEFD; ISSN:1530-6984. (American Chemical Society)The recent emergence of a wide variety of 2-dimensional materials has created new opportunities for device concepts and applications. In particular, the availability of semiconducting transition metal dichalcogenides, in addn. to semimetallic graphene and insulating boron nitride, has enabled the fabrication of "all 2-dimensional" van der Waals heterostructure devices. Furthermore, the concept of van der Waals heterostructures has the potential to be significantly broadened beyond layered solids. For example, mol. and polymeric org. solids, whose surface atoms possess satd. bonds, are also known to interact via van der Waals forces and thus offer an alternative for scalable integration with 2-dimensional materials. Here, the authors demonstrate the integration of an org. small mol. p-type semiconductor, pentacene, with a 2-dimensional n-type semiconductor, MoS2. The resulting p-n heterojunction is gate-tunable and shows asym. control over the antiambipolar transfer characteristic. In addn., the pentacene/MoS2 heterojunction exhibits a photovoltaic effect attributable to type II band alignment, which suggests that MoS2 can function as an acceptor in hybrid solar cells.
- 10Rockson, T. K.; Baek, S.; Jang, H.; Oh, S.; Choi, G.; Choi, H. H.; Lee, H. S. Macroscopic Interfacial Property as a Determining Parameter for Reliable Prediction of Charge Mobility in Organic Transistors. J. Phys. Chem. C 2018, 122, 17695– 17705, DOI: 10.1021/acs.jpcc.8b05959
- 11Wang, Q.; Jiang, S.; Qiu, L.; Qian, J.; Ono, L. K.; Leyden, M. R.; Wang, X.; Shi, Y.; Zheng, Y.; Qi, Y. Interfacial Flat-Lying Molecular Monolayers for Performance Enhancement in Organic Field-Effect Transistors. ACS Appl. Mater. Interfaces 2018, 10, 22513– 22519, DOI: 10.1021/acsami.8b07095[ACS Full Text], [CAS], Google Scholar11https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC1cXhtFSgsrnF&md5=e06dd5cbd4beafbc91108fb44f5b6634Interfacial flat-lying molecular monolayers for performance enhancement in organic field-effect transistorsWang, Qijing; Jiang, Sai; Qiu, Longbin; Qian, Jun; Ono, Luis K.; Leyden, Matthew R.; Wang, Xinran; Shi, Yi; Zheng, Youdou; Qi, Yabing; Li, YunACS Applied Materials & Interfaces (2018), 10 (26), 22513-22519CODEN: AAMICK; ISSN:1944-8244. (American Chemical Society)Org. field-effect transistors (OFETs) are the most fundamental device units in org. electronics. Interface engineering at the semiconductor/dielec. interface is an effective approach for improving device performance, particularly for enhancing charge transport in conducting channels. Here, the authors report flat-lying mol. monolayers that exhibit good uniformity and high crystallinity at the semiconductor/dielec. interface, deposited through slow thermal evapn. Transistor devices achieve high carrier mobility up to 2.80 cm2 V-1 s-1, which represents a remarkably improvement in device performance compared with devices that are completely based on fast-evapd. films. Interfacial flat-lying monolayers benefit charge transport by suppressing the polarization of dipoles and narrowing the broadening of trap d. of states. The work provides a promising strategy for enhancing the performance of OFETs by using interfacial flat-lying mol. monolayers.
- 12Gottardi, S.; Toccoli, T.; Iannotta, S.; Bettotti, P.; Cassinese, A.; Barra, M.; Ricciotti, L.; Kubozono, Y. Optimizing Picene Molecular Assembling by Supersonic Molecular Beam Deposition. J. Phys. Chem. C 2012, 116, 24503– 24511, DOI: 10.1021/jp304561s[ACS Full Text], [CAS], Google Scholar12https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC38XhsFOltr7O&md5=b828dd01f9b30975ddbe8404bc6a453dOptimizing Picene Molecular Assembling by Supersonic Molecular Beam DepositionGottardi, Stefano; Toccoli, Tullio; Iannotta, Salvatore; Bettotti, Paolo; Cassinese, Antonio; Barra, Mario; Ricciotti, Laura; Kubozono, YoshihiroJournal of Physical Chemistry C (2012), 116 (46), 24503-24511CODEN: JPCCCK; ISSN:1932-7447. (American Chemical Society)Here we report an investigation of the growth of picene by supersonic mol. beam deposition on thermal silicon oxide and on a self-assembled monolayer of hexamethyldisiloxane (HMDS). In both cases film morphol. shows a structure with very sharp island edges and well-sepd. islands which size and height depend on the deposition conditions. Picene films growth on bare silicon covered with hydrophobic HDMS shows islands characterized by large regular crystallites of several micrometers; on the other hand, films growth on silicon oxide shows smaller and thicker islands. We analyzed the details of the growth model and describe it as a balancing mechanism involving the weak interaction between mols. and surface and the strong picene-picene interaction that leads to a different Schwoebel-Ehrlich barrier in the first layer with respect to the successive one. Finally, we study the charge transport properties of these films by fabricating field-effect transistors devices in both top and bottom contact configuration. We notice that substrate influences the elec. properties of the device and we obtained a max. mobility value of 1.2 cm2 V-1 s-1 measured on top contact devices in air.
- 13Käfer, D.; Ruppel, L.; Witte, G. Growth of Pentacene on Clean and Modified Gold Surfaces. Phys. Rev. B 2007, 75, 085309 DOI: 10.1103/PhysRevB.75.085309[Crossref], [CAS], Google Scholar13https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD2sXislarur0%253D&md5=0c6a3128acc3c811a7575ed3c79fff9fGrowth of pentacene on clean and modified gold surfacesKafer, Daniel; Ruppel, Lars; Witte, GregorPhysical Review B: Condensed Matter and Materials Physics (2007), 75 (8), 085309/1-085309/14CODEN: PRBMDO; ISSN:1098-0121. (American Physical Society)The growth and evolution of pentacene films on Au substrates were studied. By combining complementary techniques including scanning tunneling microscopy, at. force microscopy, SEM, near-edge x-ray-absorption fine structure, and x-ray diffraction, the mol. orientation, cryst. structure, and morphol. of the org. films were characterized as a function of film thickness and growth parameters (temp. and rate) for different Au substrates ranging from Au(111) single crystals to polycryst. Au. Also, the influence of precoating the various Au substrates with self-assembled monolayers (SAM's) of organothiols with different chem. terminations was studied. On bare Au the growth of pentacene films is characterized by a pronounced dewetting while the mol. orientation within the resulting cryst. 3-dimensional islands depends distinctly on the roughness and cleanliness of the substrate surface. After completion of the 1st wetting layer where mols. adopt a planar orientation parallel to the surface the mols. continue to grow in a tilted fashion: on Au(111) the long mol. axis is oriented parallel to the surface while on polycryst. Au it is upstanding oriented and thus parallels the cryst. orientation of pentacene films grown on SiO2. On SAM pretreated Au substrates the formation of a wetting layer is effectively suppressed and pentacene grows in a quasi-layer-by-layer fashion with an upstanding orientation leading to rather smooth films. The latter growth mode is obsd. independently of the chem. termination of the SAM's and the roughness of the Au substrate. Possible reasons for the different growth mechanism as well as consequences for the assignment of spectroscopic data of thin pentacene film are discussed.
- 14Hasegawa, Y.; Yamada, Y.; Hosokai, T.; Koswattage, K. R.; Yano, M.; Wakayama, Y.; Sasaki, M. Overlapping of Frontier Orbitals in Well-Defined Dinaphtho[2,3-b:2′,3′-f]Thieno[3,2- b ]-Thiophene and Picene Monolayers. J. Phys. Chem. C 2016, 120, 21536– 21542, DOI: 10.1021/acs.jpcc.6b06838
- 15Chen, S.-W.; Sang, I.-C.; Okamoto, H.; Hoffmann, G. Adsorption of Phenacenes on a Metallic Substrate: Revisited. J. Phys. Chem. C 2017, 121, 11390– 11398, DOI: 10.1021/acs.jpcc.7b01806[ACS Full Text], [CAS], Google Scholar15https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2sXntFaqurc%253D&md5=0084d47a09467a7192a2141428c146beAdsorption of Phenacenes on a Metallic Substrate: RevisitedChen, Song-Wen; Sang, I-Chen; Okamoto, Hideki; Hoffmann, GermarJournal of Physical Chemistry C (2017), 121 (21), 11390-11398CODEN: JPCCCK; ISSN:1932-7447. (American Chemical Society)Phenacenes represent a class of simple hydrocarbons with appealing phys. properties ranging from high charge mobility to supercond. in combination with chem. robustness that are easily modified to serve as versatile building blocks for tailored structures. As a promising candidate for applications in org. devices, phenacenes are the focus of recent investigations. Thereby, the initial growth behavior starting from a single mol. is controversial. Here, we address the growth of [7]phenacene and [9]phenacene on a Ag(111) surface, studying the details of the initial stage of growth by scanning tunneling microscopy. According to our results, a previously introduced model involving a coverage-dependent phase change with the out-of-plane rotation of mols. in the initial growth stage can be disregarded. Instead, we find evidence for the formation of a new phase on top of an in-plane wetting layer during the initial stage of growth.
- 16Dreher, M.; Bischof, D.; Widdascheck, F.; Huttner, A.; Breuer, T.; Witte, G. Interface Structure and Evolution of Dinaphthothienothiophene (DNTT) Films on Noble Metal Substrates. Adv. Mater. Interfaces 2018, 1800920 DOI: 10.1002/admi.201800920
- 17Hanke, F.; Björk, J. Structure and Local Reactivity of the Au(111) Surface Reconstruction. Phys. Rev. B 2013, 87, 235422 DOI: 10.1103/PhysRevB.87.235422[Crossref], [CAS], Google Scholar17https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC3sXht1ClsL%252FI&md5=b9d87b94f06d5ca1a32379398b711b5dStructure and local reactivity of the Au(111) surface reconstructionHanke, Felix; Bjork, JonasPhysical Review B: Condensed Matter and Materials Physics (2013), 87 (23), 235422/1-235422/6CODEN: PRBMDO; ISSN:1098-0121. (American Physical Society)The close-packed (111) surface of gold is well known to show a 22 × √3 reconstruction on single nm lengths with a long-range herringbone pattern on scales of a few hundred nm. Here we investigate the local reconstruction using d. functional theory and compare the results to scanning tunneling microscopy expts. Moreover, we use hydrogen and fluorine as probe atoms to investigate changes in the ability of the Au(111) surface to catalyze the reactions involved in the formation of mol. nanostructures. We find a small variation of the reactivity across different surface sites and link those results to the local coordination environment of the face-centered-cubic (fcc), hexagonal-close-packed (hcp), and ridge regions. Finally, we scrutinize a commonly used approxn. in d. functional studies, namely that Au(111) is atomically flat and a perfect termination of the fcc lattice.
- 18Halgren, T. A. Merck Molecular Force Field. I. Basis, Form, Scope, Parameterization, and Performance of MMFF94. J. Comput. Chem. 1996, 17, 490– 519, DOI: 10.1002/(SICI)1096-987X(199604)17:5/6<490::AID-JCC1>3.0.CO;2-P[Crossref], [CAS], Google Scholar18https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADyaK28XhvVGmsbk%253D&md5=56fb073477b4f49d1dfbd786fc56a480Merck molecular force field. I. Basis, form, scope, parameterization, and performance of MMFF94Halgren, Thomas A.Journal of Computational Chemistry (1996), 17 (5 & 6), 490-519CODEN: JCCHDD; ISSN:0192-8651. (Wiley)This article introduces MMFF94, the initial published version of the Merck mol. force field (MMFF). It describes the objectives set for MMFF, the form it takes, and the range of systems to which it applies. This study also outlines the methodol. employed in parameterizing MMFF94 and summarizes its performance in reproducing computational and exptl. data. Though similar to MM3 in some respects, MMFF94 differs in ways intended to facilitate application to condensed-phase processes in mol.-dynamics simulations. Indeed, MMFF94 seeks to achieve MM3-like accuracy for small mols. in a combined "org./protein" force field that is equally applicable to proteins and other systems of biol. significance. A second distinguishing feature is that the core protion of MMFF94 has primarily been derived from high-quality computational data-ca. 500 mol. structures optimized at the HF/6-31G* level, 475 structures optimized at the MP2/6-31G* level, 380 MP2/6-31* structures evaluated at a defined approxn. to the MP4SDQ/TZP level, and 1450 structures partly derived from MP2/6-31G* geometries and evaluated at the MP2/TZP level. A third distinguishing feature is that MMFF94 has been parameterized for a wide variety of chem. systems of interest to org. and combinations of functional groups for which little, if any, useful exptl. data are available. The methodol. used in parameterizing MMFF94 represents a fourth distinguishing feature. Rather than using the common "functional group" approach, nearly all MMFF parameters have been detd. in a mutually consistent fashion from the full set of available computational data. MMFF94 reproduces the computational data used in its parameterization very well. In addn., MMFF94 reproduces exptl. bond lengths (0.014 Å root mean square [rms]), bond angles (1.2° rms), vibrational frequencies (61 cm-1 rms), conformational energies (0.38 kcal/mol rms), and rotational barriers (0.39 kcal/mol rms) very nearly as well as does MM3 for comparable systems. MMFF94 also describes intermol. interactions in hydrogen-bonded systems in a way that closely parallels that given by the highly regarded OPLS force field.
- 19Yano, M.; Okada, R.; Endo, M.; Shimizu, R.; Hasegawa, Y.; Yamada, Y.; Sasaki, M. Microscopic Structure of K-Doped Organic Monolayers. e-J. Surf. Sci. Nanotechnol. 2014, 12, 330– 333, DOI: 10.1380/ejssnt.2014.330[Crossref], [CAS], Google Scholar19https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2cXhs12ksrjL&md5=c8dc3473413fd364d8c47c2666b6e5b6Microscopic structure of K-doped organic monolayersYano, Masahiro; Okada, Ryosuke; Endo, Megumi; Shimizu, Ryosuke; Hasegawa, Yuri; Yamada, Yoichi; Sasaki, Masahiroe-Journal of Surface Science and Nanotechnology (2014), 12 (), 330-333CODEN: SSNUA9; ISSN:1348-0391. (Surface Science Society of Japan)Potassium (K) adsorption on coronene, picene and [6]phenacene monolayers, which serves as a model system for the metal-intercalated arom. superconductors, was studied in a mol. scale. Scanning tunneling microscopy (STM) on the K-doped monolayers revealed drastic rearrangements of the mol. layers. Besides the overall similarity of the mol. arrangement in the doped phase, fine structures and unit cell sizes were different, depending on the host mols. The overall similarity in the structures of the K-doped monolayers should be in close relation to the supercond. on these systems.
- 20Wang, Q.; Xin, Q.; Wang, R.-B.; Oehzelt, M.; Ueno, N.; Kera, S.; Duhm, S. Picene Thin Films on Metal Surfaces: Impact of Molecular Shape on Interfacial Coupling: Picene Thin Films on Metal Surfaces. Phys. Status Solidi RRL 2017, 11, 1700012 DOI: 10.1002/pssr.201700012
- 21Simbrunner, C. Epitaxial Growth of Sexi-Thiophene and Para-Hexaphenyl and Its Implications for the Fabrication of Self-Assembled Lasing Nano-Fibres. Semicond. Sci. Technol. 2013, 28, 053001 DOI: 10.1088/0268-1242/28/5/053001[Crossref], [CAS], Google Scholar21https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC3sXnsVKjsrw%253D&md5=e4bc6bf171a73f9bcd46b8dc29cfcbb9Epitaxial growth of sexi-thiophene and para-hexaphenyl and its implications for the fabrication of self-assembled lasing nano-fibresSimbrunner, ClemensSemiconductor Science and Technology (2013), 28 (5), 053001, 31 pp.CODEN: SSTEET; ISSN:0268-1242. (IOP Publishing Ltd.)A review. Over the last few years, epitaxially grown self-assembled org. nano-structures became of increasing interest due to their high potential for implementation within opto-electronic devices. Exemplarily, the epitaxial growth of the rod-like mols. para-hexaphenyl (p-6P) and α-sexi-thiophene (6T) is discussed within this review. Both mols. tend to crystallize in highly asym. elongated entities which are also called nano-fibers. It is demonstrated that the obtained needle orientations and morphologies result from a complex interplay between various parameters, e.g., substrate surface symmetry, mol. adsorption, crystal structure and contact plane. The interplay and its implications on the fabrication of self-assembled waveguiding nano-fibers and optical resonator structures are discussed and substantiated by a comparison with the reported literature. In further consequence, it is demonstrated that a precise control on the mol. adsorption geometry and the crystal contact plane represents a fundamental key parameter for the fabrication of self-assembled nano-fibers. As both parameters are basically detd. by the chosen mol.-substrate material couple, the possible spectrum of mol. building blocks for the fabrication of waveguiding and lasing nano-structures can be predicted by the discussed growth model. A possible expansion of this common valid concept is presented by the utilization of org.-org. heteroepitaxy. Based on the reported p-6P/6T heterostructures which have been fabricated on various substrate surfaces, it is substantiated that the fabrication of org.-org. interfaces can be effectively used to gain control on the mol. adsorption geometry. As the proposed strategy still lacks a precise control of the obtained crystal contact plane, further strategies are discussed which potentially lead to a controlled fabrication of opto-electronic devices based on self-assembled org. nano-structures.
- 22Goto, H.; Obata, S.; Nakayama, N.; Ohta, K. CONFLEX8; Conflex: Tokyo, Japan, 2017.Google ScholarThere is no corresponding record for this reference.
- 23Müllegger, S.; Salzmann, I.; Resel, R.; Hlawacek, G.; Teichert, C.; Winkler, A. Growth Kinetics, Structure, and Morphology of Para-Quaterphenyl Thin Films on Gold(111). J. Chem. Phys. 2004, 121, 2272– 2277, DOI: 10.1063/1.1767154[Crossref], [PubMed], [CAS], Google Scholar23https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD2cXlslOmsbs%253D&md5=4074d4435fbb4334a5ff3af436432338Growth kinetics, structure, and morphology of para-quaterphenyl thin films on gold(111)Mullegger, S.; Salzmann, I.; Resel, R.; Hlawacek, G.; Teichert, C.; Winkler, A.Journal of Chemical Physics (2004), 121 (5), 2272-2277CODEN: JCPSA6; ISSN:0021-9606. (American Institute of Physics)The adsorption, desorption, and growth kinetics as well as the thin film morphol. and crystal structure of p-quaterphenyl (4P) grown under ultrahigh vacuum conditions on single cryst. Au(111) have been investigated. Thermal desorption spectroscopy (TDS) reveals two distinct first-order peaks attributed to monolayer desorption followed by a zero-order multilayer desorption. The satn. coverage of the full 4P monolayer has been quant. measured with a quartz microbalance to be 8×1013 mols./cm2. Using LEED the structures of the 0.5 and 1 ML (monolayer) adsorbates have been studied, showing highly regular arrangements of the 4P mols., which are affected by the (111) surface structure. At the transition from 0.5 to 1 ML a structural compression of the overlayer has been obsd. The behavior of thicker 4P films has been investigated by combined TDS-XPS (XPS-XPS). A temp.-induced recrystn. process at about 270 K has been obsd. for a 7 nm thick 4P film grown at 93 K, corresponding to a transition from a disordered layerlike growth to a cryst. island growth. Ex situ optical microscopy and at.-force microscopy investigations have revealed needle-shaped 4P islands. Applying x-ray diffraction the cryst. order and epitaxial relationship of the 4P films with 30 nm and 200 nm mean thicknesses have been detd.